watchOS 5.0 (build 16R364) is an official Apple over-the-air update for the Apple Watch Series 1 (42mm), released on 2018-09-12T19:18:43Z. The update package is 763.07 MB. This is a delta (partial) update that requires 4.0 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: c6041a1caa35b64753b2af964eed7eb3559004f6.zip.